Officially, Skype is not supported on 64-bit Debian. In reality, it works perfectly.
If you try to install the official .deb package, dpkg will give you an error:
root@lambda:~# dpkg -i skype-debian_126.96.36.199-1_i386.deb dpkg: error processing skype-debian_188.8.131.52-1_i386.deb (--install): package architecture (i386) does not match system (amd64) Errors were encountered while processing: skype-debian_184.108.40.206-1_i386.deb
This package works fine if the architecture check is overridden.
wget http://www.skype.com/go/getskype-linux-deb root@lambda:~# dpkg -i --force-architecture getskype-linux-deb
Since this article was written, Skype have released a proper Debian x86_64 package.